19 July, 2020

Tweaking the K2 for digital modes

My Elecraft K2 which I assembled as a kit in 2001, has mainly been a CW rig, but now I wanted to use it more for digital modes like FT8 also. That required some tweaking:
  1. Wider bandwidth in SSB filter, so I took it from 2.4 to 2.6 kHz (KI6WX)
  2. More sensitive VOX (G3RXQ)
  3. RF-filtering on audio input (G3RXQ)

All of these are modifications to the tighly packed KSB2 board shown above so it took some patience to implement them. The bandwidth modification consists in replacing six ceramic capacitors that were sitting between the crystals. The VOX sensitivity modification is done by adding a pot which can be seen in the image as it sits outside the PCB on the left-hand side. I was lucky to find a mini 5k slider pot in my junk box which fitted in. Finally the RF-filtering was done by adding an inductor of 2.5 mH (right below the 5k pot) and a decoupling capacitor.

06 July, 2020

Recognizing a CQ on the FT8 waterfall

A CQ is not so hard to recognize on an FT8 waterfall display as there is a charactaristic indendation from the right early in the 15 second period. This can be seen in the three circled traces in the figure.

They show a CQ at 711 Hz with SNR 11 dB, one at 899 Hz with SNR 16 dB where my receive cursor is placed, and one at 2003 Hz with SNR 6 dB. These are fairly strong signals so it is easy to see the indendation, but in my experience it works down to almost -10 dB also if the contrast is set correctly with the slider on the display. 

Look closely and you'll see one in the period before also, at 21:15:00 (SNR 12 dB). Try this the next time you run FT8 and I'm sure you'll recognize it too!

27 April, 2020

GPS Clock with Binary Display

Some years ago I started making a GPS Clock with a 20 by 4 LCD, Yet another Arduino clock. It has been running since then as my shack clock. Now was the time for some additional functions, in the form of fancy variations of how to show time. I wanted a display coded in 0's and 1's, but I found that there were more than one way to do that.

The simplest one to read may be BCD (binary-coded-decimal) displays. They can be horizontally oriented like here:

10 February, 2020

Si5351 GPS corrected VFO up and running

Arduino Nano, Si5351A clock generator, I2C LCD display, and rotary encoder. The GPS signal is connected to the plug to the lower left.
I got the Si5351A Arduino controlled GPS corrected VFO designed by W3PM, Gene Marcus, up and running the other day. It gets its timing information from a QRPLabs GPS and all the functions in the original article function as they should. The main change I made was to use an LCD display running over the I2C bus, thus saving a bunch of wires from the Arduino Nano to the display.

The software worked fine except that my locator was one off in the last letter, i.e. JO59fs rather than JO59fu. I hacked the original code by adding "1" to the variable GPSlocator[5] in the calcGridSquare routine. This is not a tested fix and it may possibly have other unknown and undesirable consequences, but it works in my location.

My plan is primarily to make a 10 MHz reference oscillator out of this, as a replacement for my "Just good enough 10 MHz GPS reference" which turned out to generate too much noise in the 14 MHz band.

Now on to decide what I want to show on the 2-line display for my use and then play with Arduino code. What I definitely want is some form of indication of correction factor and thus accuracy as in the version that F2DC built.

This blog post first appeared on the LA3ZA blog.

08 October, 2019

6 m Antenna Inspiration

It's nice to see that my antenna article in Amatørradio no. 3 this year has inspired others. In no. 4, LA1AEA, Alfred, has written about how he made his own. It helped him try the 6 meter band this summer. Given his location in the very far North of Norway (Finnmark), I'm impressed by contacts that he had all the way to Greece, 3500 km away.

He writes: "LA3ZA Sverre Holm wrote an interesting article in no 3, 2019 with title "A Moxon summer antenna for 6 meter." I was inspired to try myself with some simple materials that I had available. For a long time I have considered the 6 m band to be unusable from here way up North. But this shows how wrong one can be."

This blog post first appeared on the LA3ZA blog.

14 September, 2019

QRPGuys LA3ZA Zero Beat Indicator

Image: QRPGuys.com
Some time ago QRPGuys approached me and asked if they could make the low-power zero-beat indicator that I made many years ago available as a kit. I was surprised and very honored by this request. It's been available from them for a while now and here is a description from their page:

The QRPGuys LA3ZA Zero Beat Indicator gives you a visual indication when you are tuned to the callers frequency, based on the tone of the received signal you hear on your transceiver. The theory is simple. The device takes into account the amount of built-in offset your transceiver has, usually around 300-800Hz, and illuminates an led when it detects that specific tone you hear when you are tuned to transmit on the callers specific frequency.

26 August, 2019

FT8 From My Garden With Chrome Remote Desktop

W3RW, J. Robert Wittmer wrote "Enjoy FT8 From Almost Anywhere" in the September issue of QST. He used Teamviewer for remote operation. I tried that and found what the article also said, that if the host PC's session was terminated one needed to get a new password in order for an Ipad to log on again. I also found that multiple screens was a bit cumbersome to access.

Then I read the blog of DM5HF, Christoph Steinert, and saw that Google's Chrome Remote Desktop could be a good alternative.

06 August, 2019

You have probably worked an FT8 robot

I was following the presentation of Joe Taylor, K1JT, from the recent German ham radio meeting in Friedrichshafen this year. He showed this slide of stations suspected of being robotic ones, due to them being seen on PSKReporter 24 hours a day, 7 days a week. His list is this:

I have worked many of these and most of them on multiple bands:

I only miss IK4LZH, KA1AQP, KW4SP, OO6O, OO7B, RA9H, SV1EDY, and W1KE.

In addition it wouldn't surprise me if MM0HVU also runs automatically from time to time judging from how often that call sign is seen on the bands.

Have you worked any of these stations? And are there others who are active on an almost 24/7 basis?

By the way, the presentation has title "WSJT-X FT8 and Beyond" and can be downloaded (images and sound) here. It is well worth listening too.

This blog post first appeared on the LA3ZA Radio & Electronics Blog.